Rotating device for plasma immersion supported treatment of substrates

ABSTRACT

The invention concerns a rotary drive that is suitable in particular for performing a plasma immersion-assisted treatment of three-dimensional workpieces. In this rotary apparatus ( 10 ), only the removably mounted rotatable rods ( 1, 11 ) that serve as sample holders are connected to high voltage, which is delivered via a central high-voltage lead-in ( 9 ) at the lower end of the rods, while the actual drive elements ( 7, 17 ) for rotating the rods ( 1, 11 ) are electrically insulated therefrom by suitable ceramic insulating elements ( 2, 3, 12, 13 ) FIG.  1.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a rotary apparatus for plasmaimmersion-assisted treatment, in particular ion implantation treatment,of three-dimensionally shaped workpieces, of which at least one isimmersed, within a vacuum chamber, at least temporarily into an ionizedplasma while it is exposed to a periodically pulsed high voltage, sothat the extracted ions not only react on the workpiece surface but areimplanted beneath the workpiece surface; and a treatment method usingthis rotary apparatus.

General Existing Art

[0002] In many industrial sectors today, surface properties ofproperties are already being deliberately modified by depositing orconverting thin films under vacuum. Also known, in addition todeposition methods—which apply or deposit atoms or molecules onto aproduct surface from the gas phase, or by atomization or evaporationusing a heating system, or by electron beam or arc—are non-depositionmethods such as thermal and plasma treatment in inert or reactive gases,electron and laser treatments, or the implantation of inert, reactive,nonmetallic, or metallic ions into a substrate material.

[0003] Methods and apparatuses which combine an ion or plasma treatmentwith a coating operation are already known. These methods constitute thepresent standard for low-temperature deposition of high-melting-pointalloy films which are used, for example, to protect mechanicalcomponents, e.g. highly stressed metal components, from wear, or tomodify optical components, for example camera optics and spectaclelenses. Conversion of the applied ion energy into heat is utilized inthis context. The ions are generated either in ion beam sources with orwithout mass separation, or in plasmas that either are excited inadditional plasma sources with direct current, high-frequency currentsor with microwaves, or are already present in any case in the context ofplasma-assisted coating processes.

[0004] In the aforementioned ion beam sources, ions are preacceleratedand directed onto one side of the workpieces to be treated. What isachieved thereby is a treatment or coating of substantially flatsubstrate surfaces. With the plasma technologies just mentioned,however, negative DC electrical voltages are applied to the workpieces;these voltages can range from approx. 50 V to 1 kV, and with them theions are directed, from all sides and in undirected fashion, not onlyonto substantially flat components but also onto the surface ofthree-dimensionally shaped components. At low ion energies (less than 1keV), implantation effects such as doping, nonthermal alloying ofnonequilibrium phases, interface mixing for adhesion enhancement, oraccelerated diffusion via ion beam-induced structural defects areimprobable and thus not industrially usable. For reasons ofprofitability, however, conventional ion-beam treatment (which issuitable for the purpose) is used in cost-sensitive production sectors(such as machine construction) only for specific and very limitedproduct sectors.

[0005] A new, cost-effective plasma immersion-assisted ion implantationtechnology that is the basis for the preamble of claim 1 has beendeveloped by J. Conrad, J. L. Radke, R. A. Dodd, and F. J. Worzala anddescribed in J. Applied Physics 62 (1987), p. 4591 (see also U.S. Pat.No. 4,764,394 of J. Conrad). In this so-called plasma immersion ionimplantation method, also called PII, the workpieces are immersed, aswith ion- or plasma-assisted coating, in a plasma. In contrast to thelatter method, the magnitude of the applied negative voltage is fromseveral kV to a few hundred kV, as a result of which the extracted ionsnot only react on the workpiece surface but are implanted beneath it,and initiate the aforementioned implantation effects. The high voltageis applied in the form of short pulses with a length of between severalμs and several hundred μs, at a repetition frequency of between severalhundred Hz and several kHz, in order to control heat input and at thesame time minimize the complexity of the high voltage power supply. Afurther advantage of this pulsed technique is that buildup of thecathodic plasma edge layer along the workpiece contour, in which thevoltage drop essential for ion acceleration occurs, is continuouslybeing restarted. Immediately after the pulse start, an ion bombardmentdirected in perpendicular fashion onto the particular sample surface isthus always guaranteed, even in depressions or on elevations ofstructured geometries. Insufficient or raking ion bombardment, whichoccurs in unfavorable fashion in ion beam treatments, occurs with PII atthe end of very long pulses when the plasma edge layer has expandedsufficiently far away from the plasma surface to create an envelopingplasma front that no longer follows the sample contour everywhere. Thisplasma edge layer propagates very quickly, e.g. within a fewmicroseconds.

[0006] The PII processes that have hitherto been disclosed are used onlyfor ion implantation, for example for nitriding steels or dopingsemiconductors. In this context, usually a separate plasma is generatedby autonomous DC discharge or by high-frequency or microwave excitation,and the reactive components are usually admitted into it in gaseousform.

[0007] In his aforementioned U.S. Pat. No. 4,764,394, J. Conradproposes, for carrying out the PII treatment method, an apparatus thatsubstantially has a high-vacuum treatment chamber with electricallyconductive walls, for example made of stainless steel. All theconductive walls of this chamber are electrically connected to oneanother and to ground.

[0008] A three-dimensionally shaped workpiece is placed on anelectrically conductive stationary pedestal spaced away from the chamberwalls, and the conductive pedestal is joined to an electricallyconductive support arm which holds the workpiece immovably and inelectrical contact on the pedestal. The conductive support arm iselectrically insulated from the conductive walls of the chamber by aninsulator. High-voltage pulses are delivered to the workpiece from anexternal high-voltage pulse generator via a high-voltage line that isconnected to the support arm and the pedestal.

[0009] When a high vacuum has been produced in the chamber, gas isadmitted into the chamber to form a plasma that surrounds the workpiece(immersion). This gas is a mixed gas that contains the componentsnecessary for implantation treatment. This neutral gas mixture withinthe chamber is ionized, for example, by a diffuse electron beam thatproceeds from a heating coil inside the chamber.

[0010] It should be mentioned here that the aforesaid U.S. patentmentions various other sources for the gas mixture needed for the PIItreatment, e.g. by evaporation of liquids and solids. By way of magnetelements placed outside the chamber, there is generated inside thechamber a magnetic field that deflects the diffuse electrodes proceedingfrom the electron source away from the chamber walls and into theinterior of the chamber, where they can collide with gas atoms ormolecules and ionize the gas.

[0011] The above U.S. patent mentions neither a coating treatment ofworkpieces nor the use of a large-area coating plasma as an immersionplasma. In addition, the apparatus described above and known from thisU.S. patent does not provide for rotation of the workpiece being treatedwithin the reaction chamber.

[0012] Since it is necessary, in the case of the aforementioned plasmaimmersion-assisted treatments, for high-voltage pulses of up to 100 kVto be delivered to the workpiece or workpieces within the high-vacuumtreatment chamber, movement of the workpiece by way of a rotary drive ispossible only with special designs. This is complicated, among otherfactors, by the risk of high-voltage flashovers; there is a risk inparticular of linear creepage sparks, i.e. discharges along regions inwhich metal, insulating ceramic, and plasma meet one another. Inaddition, reliable contact must be made to the moving parts, since onlydurable planar contacts make possible nonsparking delivery of voltage orcurrent

[0013] The basic idea of plasma immersion-assisted ion implantation isthat a workpiece is immersed in a plasma and then, by application of apulsed high voltage, experiences homogeneous treatment on all sides byion implantation. The use of a magnetron sputtered plasma as theimmersion plasma allows this ion implantation method to be combined withcoating techniques.

[0014] Plasma sources, but principally coating plasma sources, oftenhave a certain directional characteristic. In order to obtainhomogeneous, uniform treatment of the workpiece even in this situation,it must be moved during the process. In known coating methods, this isachieved by way of a rotary drive. Because of the pulsed high voltagethat is applied to the workpieces in the PII method, however, this hashitherto not been possible for that PII process.

OBJECT OF THE INVENTION

[0015] In view of the above, one object of the invention is to describea rotary drive for plasma immersion-assisted treatment of workpiecessuch that with it, ion implantation operations and ion-assistedlow-temperature coating operations can be performed economically, withhigh adhesion and structural quality, even on three-dimensionallystructured workpieces of complex geometry; such that multiple workpiecescan be rotated; and such that economical, homogeneous, andtemperature-stable coating using the PII treatment method is achievedwithout the risk of high-voltage flashovers, linear creepage sparking,or poor high-voltage delivery.

[0016] An apparatus achieving the aforesaid object for rotating at leastone workpiece, in particular for performing a plasma immersion-assistedtreatment, is characterized in that said apparatus has:

[0017] at least one rotatably driven sample holder in the form of arotatably mounted, electrically conductive sample rod;

[0018] a rotary drive that engages on each sample rod in order to rotateit;

[0019] a high-voltage lead-in that delivers high voltage to the samplerod; and

[0020] at least first insulating means which insulate the sample rod(11) from the rotary drive in a manner withstanding high voltage (claim1).

[0021] The fundamental idea of the design of the rotary drive accordingto the present invention is that the entire apparatus is not athigh-voltage potential, but rather that the actual driving and movingparts are at low-voltage potential, e.g. grounded, in a floating ordefined state at up to the 1000 volt level. The insulating means whichare provided between the sample rods and the other driving and movingparts, and whose dimensions depend on the maximum voltage, electricallyseparate the sample rods, which serve to attach the workpieces, from theother parts of the apparatus. Contacting and delivery of high voltage tothe sample rod or rods is accomplished at the other end thereof viaplanar wiper contacts.

[0022] Further features and advantages of the rotary drive according tothe present invention, and a method using it, are specified in theapparatus claims dependent on claim 1 and in further method claims.

[0023] Described below is an embodiment of the rotary drive usable forplasma immersion-assisted treatment in particular of three-dimensionalworkpieces, with reference to the drawings, and then exemplaryembodiments of the method according to the present invention.

[0024] A preferred embodiment of a rotary drive suitable for performinga plasma immersion-assisted treatment in particular of three-dimensionalworkpieces is described below with reference to FIG. 1, whichschematically shows an overall view of the rotary drive, and FIG. 2,which shows in schematic and enlarged fashion, partially in section,details of a ceramic insulating element that is arranged at the lowerend of each sample rod and serves simultaneously as pivot bearing andhigh-voltage lead-in.

[0025] In the case of the rotary drive depicted schematically in FIG. 1and labeled generally with the number 10, the power transfer forrotation takes place at a point different from the high-voltage contact,and the entire arrangement is not at high-voltage potential, but ratheronly rods 1, 11 serving as sample holders, of which only two are shownin FIG. 1, by way of example in a parallel vertical arrangement. Insteadof a vertical position, the sample rods can, for example, also beprovided in a horizontal position. The actual driving and moving parts,on the other hand, are at low-voltage potential, e.g. grounded, infloating fashion or at a defined voltage level of up to 1000 V. Locatedfor insulation at the upper end of sample rods 1, 11, are ceramicinsulation elements 2, 12 serving as first insulating means, whosegeometrical dimensions depend on the maximum high voltage delivered tosample rods 1, 11. The rotary drive which engages at the upper end ofsample rods 1, 11 and rotates them, indicated by drive wheels depictedschematically as circles 7, 7′, 7″, 17, is thus insulated by ceramicinsulation elements 2, 12 with respect to sample rods 1, 11 that carrythe high voltage. Drive wheels 7, 7′, 7″, 17 in turn are mounted on aseparately rotatable driven turntable 6, and can be, for example,frictionally driven disks or preferably pinions driven together inpositive and nonpositive fashion by a linkage.

[0026] Ceramic insulation elements 2, 12, located at the upper end ofsample rods 1, 11 that are mounted therein centrally, vertically, andremovably, are rotated along with sample rods 1, 11. They areadditionally protected, by metal cups 4, 14 of suitable shape, fromdeposition or plasma coating.

[0027] In order for the coating plasma to be usable in the rotary driveaccording to the invention while the high-voltage pulses aresimultaneously being delivered, these shielding panels and covers,configured as metal cups, serve to protect the insulating ceramicelements from metallic (conductive) coating. These sheet-metal cups areimplemented essentially for use in coating plasmas, but can beimplemented in many different geometrical fashions. Another result ofsuch shields is that the plasma cannot reach all the parts that carryhigh voltage and result in unnecessary currents through the rotarydrive, which would cause a current load on the pulse generator andheating of the rotary drive. It is important to note, with respect tothe shielding, that the maximum voltage that can be applied dependsprincipally on the spacings between parts that carry high voltage andother parts that do not carry high voltage. In vacuum or at a workingpressure of 0.01 - 1 Pa, spacings of 10 mm are generally sufficient forvoltages well above 30 kV.

[0028] The sample rods are locked in the upper ceramic insulatingelements 2, 12 by way of bayonet fasteners (not shown). Clamps 26 and 27are indicated schematically on sample rods 1, 11 for retaining theworkpieces or samples.

[0029] The aforementioned sample rods 1, 11 are insulated at their lowerend, again by ceramic insulation elements 3, 13, with respect to a base30 that rotates in platform fashion along with turntable 6. These lowerceramic insulation elements 3, 13 are also protected against depositionand coating plasma by suitably shaped metal cups 5, 15.

[0030]FIG. 1 moreover shows a central high-voltage lead-in 9 that isguided via branches 8, 18 to the foot of sample rods 26, 27. Alsoindicated are support columns 28 which brace the entire rotary driveaway from rotatable platform 30.

[0031]FIG. 2 shows, in detail and in enlarged fashion, the combinedhigh-voltage lead-ins and bearings, arranged at the lower end of samplerods 1, 11, that are respectively attached to lower ceramic insulationelements 3 and 13. For this purpose, a metal bushing 20, preferably madeof brass or alternatively from another highly conductive material, isattached centrally to ceramic insulation element 3, 13, forming thepivot bearing for the respective sample rod 1, 11 which can rotatetherein in low-friction fashion. A graphite wiper contact pin 21, towhich high voltage is conveyed via high-voltage lead-in 8, 18 and 23 andwhich is longitudinally movable in the brass bushing and preloaded by ahelical spring 22, rests against the lower end surface of sample rods 1,11. This type of high-voltage contact is similar to the central voltagelead-in in an ignition distributor in automotive electrical systems.Here as well, voltage pulses of up to a few tens of kV are delivered tothe distributor via a graphite wiper contact.

[0032] In the case of the arrangement shown in FIG. 2, the lower endsurfaces of sample rods 1, 11 rest in planar fashion against graphitepin 21. Brass bushing 20 is connected in its lower part, by a simplecopper wire, to high-voltage line 23 that is shielded and guided ininsulated fashion in a ceramic or metal tube 8, 18.

[0033] The description above indicates clearly that much of the rotarydrive, with retainers attached thereto, is at ground or floatingpotential, and that only the eccentrically mounted sample rods 1, 11insulated therefrom in a manner withstanding high voltage, along withattachment elements 26 and 27, are connected to high voltage.

[0034] The rotary drive according to the present invention has twomotors (not shown) outside the vacuum chamber, which drive a planetarygear drive in the vacuum chamber via suitable vacuum rotary unions (alsonot shown). Two rotary movements are performed thereby: turntable 6,together with platform 30 (rotatably connected via support columns 28)and sample rods 1, 11, performs a rotary movement about a verticalrotation axis (not shown); and sample rods 1, 11 individually rotate.Although only two sample rods 1, 11 are shown in FIG. 1 by way ofexample, any desired number, e.g. eight, sample rods arranged in acircle can be provided by appropriate design of turntable 6 and drivepinions 7, 7′, 7″, 17.

[0035] With the exemplary embodiment of a rotary drive described abovewith reference to FIGS. 1 and 2 in order to perform a plasmaimmersion-assisted treatment, many workpieces can be moved in such a wayas to permit economical, homogeneous, and temperature-stable coating.Plasma immersion processes have hitherto been performed with stationaryworkpieces (see aforementioned U.S. Pat. No. 4,764,394), which ispossible with nitriding and CVD processes. In PVD processes using plasmasources with directional characteristics, homogeneous treatment ispossible only if the workpieces are moved uniformly. By moving the partsinto and out of the plasma, the rotary drive according to the inventionmakes possible temperature stabilization in the process.

[0036] Three different exemplary embodiments of plasmaimmersion-assisted substrate treatments which advantageously use theabove-described rotary drive are described below:

[0037] I.

[0038] Use of a coating plasma as an immersion plasma for ionimplantation:

[0039] Plasma of plasma-assisted coating methods from gas phases (CVD)generated by autonomous DC discharge;

[0040] Plasma of plasma-assisted coating methods from gas phases (CVD)generated by high-frequency or microwave excitation;

[0041] Gas mixtures comprising inert gases (e.g. argon), reactive gases(e.g. nitrogen, hydrocarbons, oxygen, compounds of fluorine, boron, orchlorine) and film-forming monomers (silicon compounds, hydrocarbons,metalorganics);

[0042] Plasma of plasma- or ion-assisted coating methods from solids(PVD), such as unbalanced magnetron sputtering and arc evaporation,generated by DC voltage;

[0043] ditto, generated by high-frequency discharge;

[0044] Gas mixtures comprising inert gases (e.g. argon), reactive gases(e.g. nitrogen, hydrocarbons, oxygen, compounds of fluorine, boron,silicon, or chlorine);

[0045] Plasma of combined plasma-assisted CVD/PVD processes;

[0046] Application of positive or negative high-voltage pulses,depending on the material of the workpiece being treated; voltage level1 kV - 100 kV; high-voltage pulses of variable length and frequency.

[0047] II.

[0048] Ion assistance in coating methods by immersion of the workpiecesin the coating plasma and application to the workpieces of negativehigh-voltage pulses from 1 kV to 100 kV and variable length andfrequency.

[0049] Coating and ion treatment alternately;

[0050] Coating and ion treatment simultaneously;

[0051] Combination of coating operations without ion assistance andoperations with plasma immersion ion treatment, alternately orsimultaneously.

[0052] A number of materials can be treated with the aforementionedmethods I and II according to the present invention:

[0053] Metals and metal alloys with negative high-voltage pulses;

[0054] Insulators and plastics with bipolar voltage pulses of variousvoltage levels for ion bombardments (e.g. −1 kV to −100 kV) and forremoval of the positive charge applied thereby (e.g. +0 kV to +1 kV).

[0055] III.

[0056] Implementation and of combined PVD/PII methods by applyingbipolar voltage pulses to the workpieces at various negative andpositive levels:

[0057] Arc evaporation or atomization of the surrounding cathodicallyconnected electrode surface along the unit wall occurs during positivepulses (e.g. +0 kV to +1 kV);

[0058] Plasma immersion ion treatment occurs during negative pulses(e.g. −1 kV to −100 kV).

1. An apparatus for rotating at least one workpiece, in particular forperforming a plasma immersion-assisted treatment, characterized in thatthe apparatus (10) has: at least one rotatably driven sample holder inthe form of a rotatably mounted, electrically conductive sample rod (1,11); a rotary drive (6, 7, 7′, 17) that engages on each sample rod (1,11) in order to rotate it; a high-voltage lead-in (8, 9, 18, 23) thatdelivers high voltage to the sample rod (1, 11); and at least firstinsulating means (2, 12) that insulate the sample rod(s) (1, 11) fromthe rotary drive in a manner withstanding high voltage.
 2. The apparatusas defined in claim 1 , characterized in that the rotary drive engagesat one end of the sample rod (1, 11), with interposition of the firstinsulating means (2, 12).
 3. The apparatus as defined in claim 2 ,characterized in that the first insulating means (2, 12) are eachconfigured as a ceramic insulator in which the respective sample rod (1,11) is attached in insulated and centered fashion, and which rotatesalong with the sample rod (1, 11).
 4. The apparatus as defined in one ofclaims 1 through 3, characterized in that the sample rod(s) (1, 11) ismounted at its other end in a pivot bearing (20, 21) that delivershigh-voltage potential and is insulated by second insulating means (3,13), in a manner withstanding high voltage, with respect to a platform(30).
 5. The apparatus as defined in one of the foregoing claims,characterized in that the sample rod(s) (1, 11) is or are mountedvertically between the first and second insulating means (2, 12 and 3,13), the first insulating means (2, 12) being arranged at the top andthe second insulating means (3, 13) at the bottom.
 6. The apparatus asdefined in claim 4 or 5 , characterized in that the second insulatingmeans (3, 13) are configured as ceramic support insulators, attached tothe adjacent platform (30), having a metal bushing (20) arrangedcenteredly on them which forms a pivot bearing and in which the samplerod(s) can each rotate in low-friction fashion.
 7. The apparatus asdefined in claim 6 , characterized in that a wiper contact (21) joinedto the metal bushing (20) creates a planar high-voltage contact to thesample rod(s) (1, 11).
 8. The apparatus as defined in claim 7 ,characterized in that the wiper contact (21) has a graphite pin restingagainst the end surface of the sample rod.
 9. The apparatus as definedin one of claims 1 through 8, characterized in that several parallelsample rods (1, 11) are provided for the reception of severalworkpieces, and the rotary drive has two separate drive motors as wellas separate power transfer systems, such that the sample rods (1, 11)are rotatable along with the platform (30) both individually andtogether as a group.
 10. The apparatus as defined in one of claims 1through 9, characterized in that the ceramic insulators serving asinsulation means are protected against coating in the plasma by suitablyshaped metal shielding cups and metal covers that are insulated withrespect to the sample rod(s) (1, 11) that carry high voltage.
 11. Amethod for plasma immersion-assisted treatment in particular ofthree-dimensionally shaped workpieces, characterized in that theworkpiece or workpieces are rotated during the treatment.
 12. The methodas defined in claim 11 , characterized by the provision of a coatingunit or pulsed plasma nitriding unit on which, in order to carry out themethod, the pulsed single-pole or bipolar high-voltage power supply isretrofitted onto the rotatable sample holder.
 13. The method as definedin claim 11 , characterized by the use of a rotary apparatus as definedin one of claims 1 through 10.